Will excessive rendering damage a GPU?
If your computer has proper cooling and therefore doesn't overheat, it won't damage the GPU. 

It will have an unfavorable impact on your electricity bill and carbon footprint though.

Whether a sample size that high is actually appropriate is another question. You probably don't need that many samples or there are computationally less expensive solutions to reduce noise, e.g. the denoiser.

The rendered image will take up disk space when you save it. How much it will use depends on the resolution, the image format and its settings. The higher the resolution, the larger the file. For an overview of image formats and their disk space usage, take a look at the last section of this answer.